At present, an LSI (Large Scale Integration) in which semiconductor elements are integrated has been used for various system controls and has become a basic infrastructure for society. Since the recent LSI is operated on the basis of the arithmetic processing in accordance with programs, the condition that program can be stored is indispensable in many cases, and a non-volatile memory which is one type of integrated semiconductor memories incorporated in an LSI has become extremely important as an element for satisfying the condition. Since it is required that the LSI is used for various applications by modifying the programs, the non-volatile memory which is rewritable and in which stored data are not lost even when the power of LSI is shut off is indispensable.
With regard to the non-volatile memory of a semiconductor element, for example, “Physics of Semiconductor Devices, 2nd edition”, Wiley-Interscience Pub. by S. Sze, pp. 496 to 506 (Non-Patent Document 1) describes a so-called floating gate memory and a memory using an insulator (insulator-type memory). As described herein, a memory in which insulators are laminated and charges are accumulated in the traps of the interface thereof and the insulators does not have to form a new conductive layer in comparison with the floating gate memory, and such a memory has a good matching with the CMOS (Complementary Metal Oxide Semiconductor) LSI process.
As an insulator for accumulating charges, a laminated layer of a nitride film and an oxide film has been widely used because it can achieve both the charge-trapping characteristics and the rewriting characteristics. For example, as a pioneer development example, a report by Yatsuda et al. “IEEE Transaction on Electron Devices” Vol. ED-32, No. 2, pp. 224 to 231, 1985 (Non-Patent Document 2) is known. In this report, a two-transistor cell in which a memory transistor and a select transistor are arranged in series is used. In the memory transistor, by applying bias between the channel and gate, the injection and emission of the charges into and from the whole surface of the channel are performed using F-N (Fowler-Nordheim) tunnel current and direct tunnel current.